The trend in networks towards protocols based on IP allows for mobility management through IP mechanisms, such as Mobile IP (MIP). This protocol enables a mobile to change its access point in different IP domains without changing its IP address. An IP domain may be defined as a contiguous portion of the Internet whose IP addresses belong to one and the same subnetwork. Mobility management in an IP network is based on detection of the change of access network (also called detachment network) by the mobile, the acquisition of a new IP configuration by the mobile and the registration of the new location with a central point in the network illustrated by FIG. 1, called Home Agent HA. The latter then routes the packets that arrive at the subscription network, also called home network, from the mobile to the network visited by the mobile by using an IP in IP encapsulation. However, since the mobile IP protocol is not suited to frequent changes of access points, the choice to separate macro-mobility and micro-mobility has been proposed. Micro-mobility corresponds to rapid and frequent local movements of a mobile within one and the same IP access network whereas macro-mobility corresponds to the movements of a terminal with change of IP access network. This separation makes it possible to reduce the location update delay and consequently the loss of data packets. Several protocols have adopted this choice; notable among them are the HMIP and Cellular IP protocols.
More recently, telecommunications operators have been turning towards a new mobility protocol based on the same principle as MIP, called PMIP (Proxy MIP). PMIP enables the mobility of a terminal to be taken over by the network without requiring the involvement of the terminal in the signaling interchange. The terminal must be identified with its attachment (or access) router and the latter “makes it believe” that it is still in its subscription network: the attachment router updates the location with the home agent and announces to the terminal its new default route, which is typically the IP address of the default gateway or default router.
Mobility management in a multivendor wireless network context comprises two major steps:                taking of the handoff decision to switch from an access point of a network of technology A to another access point situated in a network of technology B. This decision takes into account various parameters such as the preferences of the operator and of the user, the requirements of the applications and the network capabilities. The handoff decision is taken in the control plane.        execution of the handoff decision to take charge of the update of the mobile node location (or registration of the new location) in the network, and the updating of the routing of the user data and of the signaling to and from the new access point. The execution of the handoff takes effect in the data plane.        
Unlike the conventional telecommunication networks, the IP networks have the control plane and the data plane merged together; the signaling is in-band. This means that the data packets and the signaling to set up the route pass through the same nodes of a network. Furthermore, within IP networks, it is usually the same entity that takes the decision and executes the handoff (for example, execution of the MIP protocol by the mobile node) whereas, within telecommunication networks (operator networks), the entity that takes the handoff decision is different from the entity that executes the handoff. Also, in most cases, these entities are centralized in the network, their configuration is fixed in the network and depends on the execution protocol used.
The final decision and the final execution of the handoff can be performed according to several embodiments depending on where these functionalities are implemented, either on the network side or on the mobile side:
mode 1: handoff control by the mobile and handoff execution in the mobile. The latter can maintain profiles that take into account user/operator preferences, the characteristics of the access networks and of the applications.
mode 2: handoff control by the network (by one or more functional entities of the network, typically by means of a mobility manager or via a decision entity chain) and handoff execution in the mobile,
mode 3: handoff control by the mobile and handoff execution in the network (by one or more functional entities of the network),
mode 4: handoff control by the network (by one or more functional entities of the network) and handoff execution in the network (by one or more functional entities of the network).
The mode may be determined dynamically. Thus, some work that proceeds within the IETF recommends that the mobile node should signal to the attachment network whether it is taking charge of the execution of the handoff using the MIP protocol or whether it is asking the network to perform this execution using the PMIP protocol. According to other work, the network announces its capacity to execute the handoff using the PMIP protocol and the mobile node expresses its preference regarding the use of this service. Some 3GPP specifications relating to the new architecture of the 3GPP mobile networks (LTE/SAE) can be used to define a hierarchy of tunnels for the mobility management. A number of mobility scenarios are given depending on whether handoffs within or between 3GPP access networks or handoffs between 3GPP systems or not between 3GPP systems are being performed.
Depending on the mobility management protocols available in the network, a hierarchy of tunnels may be formed by a number of tunnels of different types. A tunnel is set up to ensure the correct routing of IP packets between two nodes by passing through routers that do not necessarily know the respective mobility protocol associated with the packets. “Tunneling” is the method of encapsulating and decapsulating an IP packet either in another IP packet (for example MIP or PMIP), or in a packet of another type (for example GTP). For example, and with reference to FIG. 1, a mobile is reachable via a specific PMIP tunnel as far as its anchor point (in this case, the Serving Gateway SGW) in the SAE (System Architecture Evolution (i.e., the network of a future generation (called 4G) according to the 3GPP guidelines)) network; it is then reachable via a specific GTP tunnel as far as its access point at the link level (in this case, eNodeB). An anchor point is the point of entry into the access network allowing the mobile to connect to other networks; the traffic between the mobile and a node of another network mandatorily passes through this anchor point.
In the case of multivendor networks, a number of handoff decision or execution modes may exist concomitantly. This in particular raises the problem of the choice of the mode and of the decision and execution entities, in mobility management. Recently, works propose retaining only two possible handoff execution modes: Proxy MIP by the network or MIP by the terminal, the mobile terminal taking the decision to activate one or other of the modes. The mobile terminal discovers that that PMIP is supported by the network and may express its desire to activate it; there is no negotiation or possible control by the network as to the choice of handoff execution protocol. For example, certain specifications retained by the 3GPP combine the use of several mobility protocols that do not offer the means of controlling the activation of one or another protocol by the control plane entities responsible for taking the handoff decision.